The present invention relates to a an endless sieve band or composite band for paper machines, or the like.
Sieve bands or composite bands of the above mentioned general type are known in the art. A known band has a plurality of helixes of elastic synthetic or metallic wire and including opposite winding legs and head curves connecting the latter with one another. A head curve of the neighboring helix is inserted into an intermediate space of its helix so that, between both helixes an overlapping region takes place, and an insertion wire of synthetic plastic material or metal is inserted in this region. Such a band is disclosed, for example, in the German Pat. No. 2,419,751 and in the German Offenlegungsschrift No. 2,938,221. The wire helixes of the band disclosed in this first reference has a pulling spring-like tensioning so as to contract the respective neighboring wire helix. Such a wire composite band must elastically maintain in operation its dimensions, particularly in the transverse direction. Furthermore, the technical progress of such a wire composite band is that its manufacture is simplified so that during their insertion into one another the helixes forcibly find their place and are clamped relative to one another; therefore, expensive arrangements can be avoided and the connecting means need no longer be rigid and heavy. In the case of the above mentioned Offenlegungsschrift, it is provided that the helixes have no pulling-spring-like tensioning and the wire of the helixes is torsion-free. The service life of the flat shaped article of this reference must be increased, and the marking mobility must be guaranteed. These different, practically contradictory requirements lead to flat shaped articles which are used in many fields. After a certain time it has, however, been shown that these bands possess characteristics which can be improved. Because of the mainly round or slightly oval identical cross sections of the wire forming the helixes, the bands have an extremely high air permeability. In many cases it is desirable, however, during the manufacture of paper, this often leads to fluttering of paper. In order to eliminate this problem, additional filling elements are introduced into the helixes of elastic synthetic plastic or metallic wire, in addition to the connecting means such as insertion wires. This permits to influence the air permeability, but includes a considerable degree of labor expense to insert into the helixes the respective parts, such as insertion wires or cotton-synthetic plastic filling means. Moreover, material consumption and selling price increase.
A further characteristic of the known sieve bands or composite bands is the so-called point contact between the supporting winding legs and, for example, the paper. Depending upon the weight and quality of the paper and the applied pressure during the manufacture of paper, this leads to impressing the winding layers onto the finished paper. Although this impression is desired, for example, for manufacture of patterns, during the manufacture of high quality smooth papers such impressions must be avoided. The point-like or edge-like contact between the supporting winding legs of the helixes and the paper leads to another characteristic of the known flat shaped articles, namely to a weak heat flow between the calender roller and the paper because of only small supporting possibilities, and thereby required small contact surfaces. This leads to the fact that the supporting winding leg possesses greater contact surfaces with the paper, whereby the danger of marking on the supporting point and the supporting edges is smaller and the heat flow is improved. However, a higher air permeability of the band must be taken into account, inasmuch as the distance between the individual windings of the helixes is greater. For reducing this air permeability, sealing guides and sheet inserts are introduced in the known flat shaped articles, extending in the longitudinal direction of the helixes or also in the intermediate spaces between the neighboring winding legs.